Transluminal coronary angioplasty involves the nonsurgical widening of a passage through an artery that has been narrowed or stenosed by deposits of plaque or plaque-ridden tissue. One approach to coronary angioplasty involves the use of a "hot tip" device which includes a heating element at the distal end of a catheter. The heating element is heated to a temperature of several hundred degrees Centigrade and is moved through a blocked artery to soften and plow through the stenotic material. Due to the high temperatures involved, the hot tip device is kept moving through the artery when it is energized to avoid overheating and burning of tissue.
The heating element in prior art hot tip devices has been metal, and electrical, catalytic and laser heating of the element are known. In the laser-energized hot tip, an optical fiber extends through the catheter and terminates in the heating element. Laser energized hot tip devices are disclosed in German Patent No. 2,826,383 published Dec. 20, 1979, U.S. Pat. No. 4,646,737 issued March 3, 1987 to Hussein et al, U.S. Pat. No. 4,662,368 issued May 5, 1987 to Hussein et al and U.S. Pat. No. 4,773,413 issued Sep. 27, 1988 to Hussein et al. In the disclosed devices, laser energy carried through the optical fiber raises the temperature of the heating element. U.S. Pat. Nos. 4,662,368 and 4,773,413 disclose a lens or window positioned in a cavity in the metal heating element. The window is made of an optically transparent material, such as quartz or sapphire. A portion of the laser energy incident on the window heats the surrounding metal, and a portion of the laser energy passes through the window to assist in heating and vaporizing the plaque.
Techniques have been proposed for distinguishing between plaque and normal tissue by stimulating fluorescence from tissue in an artery and analyzing the characteristics of the fluorescence. U.S. Pat. No. 4,785,806 issued Nov. 22, 1988 to Deckelbaum discloses the use of ultraviolet laser energy for stimulating fluorescence. Fluorescence intensity at selected wavelengths in the blue-green wavelength range is analyzed to distinguish between plaque and normal tissue. The use of a dye to enhance the contrast between the fluorescence from plaque and the fluorescence from normal tissue is disclosed in U.S. Pat. No. 4,641,650 issued Feb. 10, 1987 to Mok. The use of visible light to stimulate fluorescence from artherosclerotic plaque is disclosed in U.S. Pat. No. 4,718,417 issued Jan. 12, 1988 to Kittrell et al.
The ability to distinguish between plaque and normal tissue enables the surgeon to better control the angioplasty procedure. It is desirable to provide such diagnostic capability in hot tip devices. In the past, the heating element usually blocked the distal end of the optical fiber in hot tip devices, and optical diagnostic procedures have not been feasible.
Because of the requirement for accessing blood vessels of very small diameter, it has become commonplace in transluminal coronary angioplasty to use guidewires for controlling the placement of catheters. Catheters of sufficiently small diameter to be used in a small blood vessel typically lack the torsional rigidity to be adequately controlled as they are advanced through the vascular system to the obstructed site. Guidewires have an extremely small diameter, flexibility and sufficient torsional rigidity to be advanced to very small diameter blood vessels. The catheter is then advanced over the guidewire to the obstructed site. A steerable guidewire suitable for use in a balloon dilatation procedure is disclosed in U.S. Pat. No. 4,545,390 issued Oct. 8, 1985 to Leary and assigned to assignee of the present application.
It is a general object of the present invention to provide an improved hot tip device for coronary angioplasty.
It is another object of the present invention to provide a hot tip device having optical diagnostic capability.
It is a further object of the present invention to provide improved methods for coronary angioplasty.
It is yet another object of the present invention to provide a hot tip device wherein optical diagnostic procedures can be performed through the heating element.
It is still another object of the present invention to provide a hot tip device having a filter glass heating element which absorbs a first range of wavelengths and passes a second range of wavelengths.